The subject matter of the present invention essentially relates to a surface for transferring a more or less viscous liquid product such, for example ink to any support whatsoever, for example, as paper.
It is also directed to a method of manufacturing such a surface.
It is further directed to a printing blanket provided with this surface and usable for example, in offset printing.
There has already been proposed a very great number of blanket structures for offset printing. As known, printing cylinders are generally covered or lined with such a blanket to allow printing upon a sheet of paper, for instance, and which receive the ink carried by a litho offset plate, itself carried by a cylinder or roll which has previously been covered with a film of ink and water.
The inconveniences and problems or difficulties encountered with these structures are the following.
At first, the transfer of ink upon the blanket of the printing cylinder is not -carried out in a precise manner. In other words, the transfer of the inked pattern, design or of the inked relief upon the blanket is not carried out in a faithful or accurate manner since the ink has the tendency to spread out over the blanket of the printing cylinder and to diffuse thereby seriously affecting the quality of the printing upon the paper. These defects are particularly marked in areas printed with screening, i.e., images consisting of points or printed areas separated from each other by non-printing zones. Moreover the transfer of ink upon the printing blanket is not regular so that a heterogeneousness may be seen in the tint areas, i.e., the printed zones consisting of a continuous film of ink, i.e., fully covering a certain surface.
Likewise, the blankets of the prior art do not provide a good cleaving, splitting, or separation of the ink-water pair transferred upon the printing blanket, thereby reflecting upon the printing made by the blanket upon the paper. In other words, the selectivity of the positioning of the ink and of the water upon the blanket is crucial if it is desired to obtain, on the paper, a printed image with an outstanding quality.
It should further be pointed out that when leaving the printing, i.e., at the level of the contact zone between the blanket-carrying cylinder and the underlying back pressure cylinder high cleaving forces are generated cause a bad release of the paper in view of too great a relative adherence between the ink and the surface of the blanket. Owing to this relatively substantial adherence, fibres may come off the paper sheet and thus be caused to gather upon the very blanket during the printing, gradually impairing the quality of printing.
The object of the invention is therefore, in particular, to remedy the inconveniences referred to hereinabove by proposing an improved transfer surface providing an outstanding quality of the image transferred upon the paper, a regular transfer of ink upon the blanket as regards the tint areas, a good ink-water cleaving on the surface of the blanket and an outstanding release of the paper when leaving the printing without any risk of accumulating or gathering paper fibres upon the blanket.
For that purpose, the subject of the invention is a surface of a more or less viscous liquid product upon a support to be covered such as paper for example, characterized in that it consists of a substrate upon which are grafted or inserted a plurality of distinct zones consisting either of zones from an anti-adhesive or anti-adherent material or of zones made from a hydrophilic material or of zones made from a hydrophobic material or of any combination of such zones to impart upon the said surface a heterogeneousness of structure to improve the quality of the transfer upon the support.
The aforesaid anti-adhesive or anti-adherent material is silicone, forming upon the substrate a plurality of zones, all of which represent from 5% to 95% of the surface area of the said substrate.
The hydrophilic material is a polymer of the kind, for example, with acid lateral groups forming on the substrate a plurality of zones, all of which represent from 5% to 95% of the surface area of the substrate.
The hydrophobic material is a non-polar or fluorine-containing, polymer forming on the substrate a plurality of zones, all of which represent from 5% to 95% of the surface area of the substrate.
According to an exemplary embodiment, the aforesaid transverse surface comprises a substrate on which are grafted or inserted zones of anti-adherent or anti-adhesive material representing from 5% to 50% of the surface area of the substrate, zones of hydrophilic material representing from 5% to 75% of the surface area of the substrate, and zones of hydrophobic material representing from 5% to 75% of the surface area of the said substrate.
Preferably the aforesaid zones of anti-adherent materials, of hydrophilic material, and of hydrophobic material represent from 5% to 10%, from 30% to 45% and from 50% to 60%, respectively, of the surface area of the substrate.
According to another characterizing feature of this transfer surface, the aforesaid zones have any geometrical shape providing a regular or random screening upon the substrate.
It should further be specified here that the surface area of insertion of each zone upon the aforesaid substrate ranges between about 10xe2x88x927 mm2 and about 10xe2x88x922 mm2.
According to still another characterizing feature of this invention, the aforesaid substrate itself is a hydrophilic or hydrophobic material, preferably of an elastomeric nature.
The invention is further directed to a method of manufacturing a surface for the transfer of a more or less viscous liquid product meeting either one of the characterizing features referred to hereinabove, this method being characterized in that it consists in photochemically grafting upon a substrate anti-adherent, hydrophilic or hydrophobic monomers or oligomers or any combination of such monomers or oligomers to provide upon the substrate distinct zones imparting upon the surface a heterogeneousness of structure capable of improving the quality of the transfer.
This method is further characterized in that the aforesaid zones are provided after coating of the monomers or oligomers upon the substrate, by irradiation of the latter through a mask comprising opaque and transparent portions.
The grafting of the aforesaid zones may be carried out by successive irradiations with different masks and in any order whatsoever.
It should further be specified here that the irradiation is performed for example, by means of an ultraviolet radiation and in the presence of at least one photo-initiator.
This invention is further directed to a printing blanket which comprises a transfer surface complying with the characterizing features referred to hereinabove or obtained by means of the method set forth hereinabove.
This blanket may present itself as a strip or web or as a sleeve adapted to be mounted onto a printing cylinder in a web-fed rotary offset printing machine for example.